58 lines
2.2 KiB
Rust
58 lines
2.2 KiB
Rust
// SPDX-License-Identifier: Apache-2.0 OR MIT
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// Adapted from https://github.com/Rahix/avr-device.
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//
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// Refs:
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// - AVR Instruction Set Manual https://ww1.microchip.com/downloads/en/DeviceDoc/AVR-InstructionSet-Manual-DS40002198.pdf
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#[cfg(not(portable_atomic_no_asm))]
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use core::arch::asm;
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pub(super) type State = u8;
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/// Disables interrupts and returns the previous interrupt state.
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#[inline]
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pub(super) fn disable() -> State {
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let sreg: State;
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// SAFETY: reading the status register (SREG) and disabling interrupts are safe.
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// (see module-level comments of interrupt/mod.rs on the safety of using privileged instructions)
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unsafe {
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// Do not use `nomem` and `readonly` because prevent subsequent memory accesses from being reordered before interrupts are disabled.
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// Do not use `preserves_flags` because CLI modifies the I bit of the status register (SREG).
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// Refs: https://ww1.microchip.com/downloads/en/DeviceDoc/AVR-InstructionSet-Manual-DS40002198.pdf#page=58
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#[cfg(not(portable_atomic_no_asm))]
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asm!(
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"in {0}, 0x3F",
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"cli",
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out(reg) sreg,
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options(nostack),
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);
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#[cfg(portable_atomic_no_asm)]
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{
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llvm_asm!("in $0, 0x3F" : "=r"(sreg) ::: "volatile");
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llvm_asm!("cli" ::: "memory" : "volatile");
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}
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}
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sreg
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}
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/// Restores the previous interrupt state.
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///
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/// # Safety
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///
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/// The state must be the one retrieved by the previous `disable`.
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#[inline]
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pub(super) unsafe fn restore(sreg: State) {
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// SAFETY: the caller must guarantee that the state was retrieved by the previous `disable`,
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unsafe {
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// This clobbers the entire status register. See msp430.rs to safety on this.
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//
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// Do not use `nomem` and `readonly` because prevent preceding memory accesses from being reordered after interrupts are enabled.
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// Do not use `preserves_flags` because OUT modifies the status register (SREG).
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#[cfg(not(portable_atomic_no_asm))]
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asm!("out 0x3F, {0}", in(reg) sreg, options(nostack));
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#[cfg(portable_atomic_no_asm)]
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llvm_asm!("out 0x3F, $0" :: "r"(sreg) : "memory" : "volatile");
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}
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}
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